Liquid air cycle engine
A liquid air cycle engine (LACE) is a type of
In a
LACE was studied to some extent in the USA during the late 1950s and early 1960s, and by late 1960 Marquardt had a testbed system running. However, as NASA moved to ballistic capsules during Project Mercury, funding for research into winged vehicles slowly disappeared, and LACE work along with it.
LACE was also the basis of the engines on the British Aerospace HOTOL design of the 1980s, but this did not progress beyond studies.[dubious ][citation needed]
Principle of operation
Conceptually, LACE works by compressing and then quickly liquefying the air. Compression is achieved through the ram-air effect in an intake similar to that found on a high-speed aircraft like Concorde, where intake ramps create shock waves that compress the air. The LACE design then blows the compressed air over a heat exchanger, in which the liquid hydrogen fuel is flowing. This rapidly cools the air, and the various constituents quickly liquefy. By careful mechanical arrangement the liquid oxygen can be removed from the other parts of the air, notably water, nitrogen and carbon dioxide, at which point the liquid oxygen can be fed into the engine as usual. It will be seen that heat-exchanger limitations always cause this system to run with a hydrogen/air ratio much richer than stoichiometric with a consequent penalty in performance[1] and thus some hydrogen is dumped overboard.
Advantages and disadvantages
The use of a winged launch vehicle allows using
In order to appreciably reduce the mass of the oxygen carried at launch, a LACE vehicle needs to spend more time in the lower atmosphere to collect enough oxygen to supply the engines during the remainder of the launch. This leads to greatly increased vehicle heating and drag losses, which therefore increases fuel consumption to offset the drag losses and the additional mass of the
Other issues are introduced by the relative material and logistical properties of
Most significantly, the LACE system is far heavier than a pure rocket engine having the same thrust (air-breathing engines of
Thus, the advantages, or disadvantages, of the LACE design continue to be a matter of some debate.
History
LACE was studied to some extent in the United States of America during the late 1950s and early 1960s, where it was seen as a "natural" fit for a winged spacecraft project known as the Aerospaceplane. At the time the concept was known as LACES, for Liquid Air Collection Engine System. The liquified air and some of the hydrogen is then pumped directly into the engine for burning.
When it was demonstrated that it was relatively easy to separate the oxygen from the other components of air, mostly nitrogen and carbon dioxide, a new concept emerged as ACES for Air Collection and Enrichment System. This leaves the problem of what to do with the leftover gasses. ACES injected the nitrogen into a ramjet engine, using it as additional working fluid while the engine was running on air and the liquid oxygen was being stored. As the aircraft climbed and the atmosphere thinned, the lack of air was offset by increasing the flow of oxygen from the tanks. This makes ACES an ejector ramjet (or ramrocket) as opposed to the pure rocket LACE design.
Both Marquardt Corporation and General Dynamics were involved in the LACES research. However, as NASA moved to ballistic capsules during Project Mercury, funding for research into winged vehicles slowly disappeared, and ACES along with it.
See also
- Air-augmented rocket
- RB545
- Reaction Engines SABRE - a precooled jet enginethat cools but does not liquefy the air
- Scramjet
References
- ^ "Archived copy" (PDF). Archived from the original (PDF) on 2015-02-13. Retrieved 2019-05-27.
{{cite web}}
: CS1 maint: archived copy as title (link) - ^ Orloff, Benjamin. A Comparative Analysis of Singe-State-To-Orbit Rocket and Air-Breathing Vehicles (PDF). AFIT/GAE/ENY/06-J13. Archived (PDF) from the original on June 4, 2011.
- ^ "LOX/LH2: Properties and Prices". Archived from the original on March 13, 2002.
- ^ "Liquid Air Cycle Rocket Equation, Henry Spencer Comment".